1. Field of the Invention
The present invention relates to a sampling device for a gas analyzer and, more particularly, to such a sampling device which samples a gas at a constant rate.
2. Description of the Prior Art
Gas chromatography is a procedure for analyzing exhaust gas from an engine of, for example, an automobile. The procedure generally requires the exhaust gas to be diluted with air and then sampled at a constant rate by means of a constant-volume sampling device. There are several methods for sampling the diluted exhaust gas.
The bag method diverts a sample of the diluted exhaust gas into a tetrabag by means of the constant-volume sampling device. The sample is generally uniform in concentration. Although the bag method is relatively simple, it does, however, have disadvantages in that not only is it difficult to apply the method to high-boiling-point components and highly-absorbent substances, but also the results of the method are apt to be influenced by the background of the bag itself.
Another method for sampling the diluted exhaust gas is the batch method. In this method the constant-volume sampling device collects a sample of the diluted exhaust gas in an absorbent solution or material during a drive mode. Although the exhaust gas sample in the batch method is uniformly concentrated, this method is disadvantageous in not only that the concentrated exhaust gas sample requires treatment, such as extraction and heating, prior to analysis, but also that considerable skill and time are required to perform this procedure.
Yet another method for sampling the diluted exhaust gas is the continuous measuring method. In this method the constant-volume sampling device introduces the diluted exhaust gas into a gas sampling loop. The sample of diluted exhaust gas is then equilibrated to atmospheric pressure which is followed by the introduction of a carrier gas or the like for gas chromatography. Although this method is generally simple and accurate, a drawback of this method is that only an instantaneous measurement can be achieved during the sampling; therefore, analysis of the drive mode cannot be achieved.
Therefore, there remains an unfulfilled need in the art of gas chromatography for a sampling device which is able to sample a diluted exhaust gas without the numerous drawbacks mentioned above.